1. Field of the Invention
The present invention relates to a physical quantity sensor device and a method of adjusting the physical quantity sensor device.
2. Description of the Background Art
Heretofore, as a physical quantity sensor device, for example, a digital computation type of physical quantity sensor device, which corrects an output value of a physical quantity sensor element by converting an analog signal, output from the physical quantity sensor element, to a digital signal with an A/D converter (ADC: Analog-to-Digital Converter) and carrying out a computation using a digital computing circuit such as a CPU (Central Processing Unit) or a DSP (Digital Signal Processor), is known.
As the physical quantity sensor device, the present inventors propose the following device. After a second-order first characteristic expression showing a corrected output characteristic of a physical quantity sensor (sensor element) is calculated, and a first characteristic value is extracted, based on an initial output value and target output value of the physical quantity sensor, a second characteristic expression for correcting the first characteristic value is calculated, and a second characteristic value is extracted, based on a predetermined temperature and the first characteristic value. Further, the corrected output value of the physical quantity sensor is computed based on the first characteristic expression corrected by inputting the second characteristic value into the second characteristic expression, and a result of the computation is output as a digital signal (for example, refer to WO2013/100156).
A detailed description will be given of the physical quantity sensor device of WO2013/100156. FIG. 9 is a block diagram showing a functional configuration of a heretofore known physical quantity sensor device. A heretofore known physical quantity sensor device 1100 is an integrated circuit (IC) configured of a physical quantity sensor 1101, a temperature sensor (sensor element) 1102, a Vcc voltage divider section 1103, a computing section 1104, a storage section 1105, and an input/output section 1106. A setting device 1110 calculates initial setting information (first and second characteristic values) for correcting an output value of the physical quantity sensor device 1100, and outputs the initial setting information to the input/output section 1106 of the physical quantity sensor device 1100.
The physical quantity sensor 1101 is a sensor element which generates an output signal corresponding to the physical quantity of a detected measuring medium. The Vcc voltage divider section 1103 divides a power supply voltage supplied via a Vcc terminal. The computing section 1104 calculates a corrected output value of the physical quantity sensor 1101 based on an output value of the physical quantity sensor 1101, an output value of the temperature sensor 1102, and the initial setting information written in the storage section 1105. The input/output section 1106 outputs the corrected output value of the physical quantity sensor 1101, the output value of the temperature sensor 1102, and an output value of the Vcc voltage divider section 1103 to the exterior.
The setting device 1110 is configured of a first acquisition section 1111, a second acquisition section 1112, a first calculation section 1113, a second calculation section 1114, and an input/output section 1115. The first acquisition section 1111 acquires a plurality of initial output values from the input/output section 1106 of the physical quantity sensor device 1100 via the input/output section 1115. The second acquisition section 1112 acquires a target output value of the physical quantity sensor 1101 preset so as to correspond to a plurality of initial output values of the physical quantity sensor 1101. The first and second calculation sections 1113 and 1114 calculate the first and second characteristic values respectively.
FIG. 10 is a block diagram showing one example of an overall configuration of a semiconductor physical quantity sensor device formed on a semiconductor chip by applying the invention of FIG. 9. A physical quantity sensor device 1200 is configured of a physical quantity sensor 1201, a temperature sensor 1202, a Vcc voltage divider section 1203, a computing circuit 1204, a data storage section 1205, an I/O (Input/Output) interface 1206, first to third sample holds 1211 to 1213, first and second selectors 1214 and 1219, an A/D converter 1215, and first to third latches 1216 to 1218.
The physical quantity sensor 1201, temperature sensor 1202, and Vcc voltage divider section 1203 correspond to the heretofore described physical quantity sensor 1101, temperature sensor 1102, and Vcc voltage divider section 1203 of FIG. 9. Respective output signals of the physical quantity sensor 1201, temperature sensor 1202, and Vcc voltage divider section 1203 are analog signals. The first to third sample holds 1211 to 1213, disposed in the stages subsequent to the physical quantity sensor 1201, temperature sensor 1202, and Vcc voltage divider section 1203 respectively, retrieve (sample) the respective analog signals, continuously input from the preceding stages, at regular time intervals, and hold the respective sampled analog signals for a fixed time.
The A/D converter 1215 is disposed in a stage following the first to third sample holds 1211 to 1213 via the first selector 1214. The first selector 1214 selects one of the analog signals input from the first to third sample holds 1211 to 1213 and outputs the one to the A/D converter 1215. The A/D converter 1215 converts the analog signal selected by the first selector 1214 to a digital signal, and outputs the digital signal to the computing circuit 1204. The computing circuit 1204 and data storage section 1205 correspond respectively to the heretofore described computing section 1104 and storage section 1105 of FIG. 9.
The first to third latches 1216 to 1218 hold the digital signals of the physical quantity sensor 1201, temperature sensor 1202, and Vcc voltage divider section 1203, respectively, for a fixed time. The second selector 1219 selects one of the digital signals input from the first to third latches 1216 to 1218, and outputs the one to the I/O interface 1206. The I/O interface 1206 corresponds to the heretofore described input/output section 1106 of FIG. 9 and carries out a digital signal input from the second selector 1219 and output to the exterior. Reference numerals 1221 to 1223 are a reference voltage source, a sensor drive circuit, and an oscillator respectively.
That is, the physical quantity sensor device of WO2013/100156 is of a digital output type which outputs a result of digital computation to the exterior with the result remaining as a digital signal. However, the market trend is such that a heretofore known analog output type which outputs an analog signal to the exterior is still a mainstream. The reasons include the facts that digital communication standards are not unified, the transmission rate of digital communication is lower than the transmission rate of analog communication, the rate of communication with a digital signal output to the exterior from the physical quantity sensor device (for example, the data transfer rate of an in-vehicle network (CAN: Controller Area Network or LIN: Local Interconnect Network)) is low, the digital output type is costly, and the like.
In order to solve the problems of the digital output type of physical quantity sensor device, various studies are also being made on a physical quantity sensor device in which are combined a digital computation for an improvement in correction accuracy and an analog output type with high market needs. As this kind of physical quantity sensor device, there is proposed a device wherein a flow signal analog-to-digital conversion circuit, an adjustment computing circuit, and a chip temperature sensor circuit are formed into an integrated circuit on one semiconductor chip, and a chip temperature signal output from the chip temperature sensor circuit is input into the adjustment computing circuit, thus carrying out a correction for reducing a signal processing-system temperature dependence error (for example, refer to JP-A-2003-166865).
JP-A-2003-166865 discloses a method whereby, in a flow sensor device which measures a gas flow, an output value of a flow sensor (sensor element) and an output value of a temperature sensor, disposed on the same chip as the flow sensor, are converted to respective digital signals by an A/D converter, and a corrected output value of the flow sensor is acquired using a digital computation based on information stored in a memory. The differences of the physical quantity sensor device of JP-A-2003-166865 from the physical quantity sensor device of WO2013/100156 are the following three.
The first difference is that a D/A converter (DAC: Digital-to-Analog converter) which converts a digital signal (a computation result) to an analog signal is provided between a digital computing circuit and an output terminal. The second difference is that the output terminal is for an analog output, and furthermore, that a digital I/O terminal is provided. The third difference is that items of information converted to digital signals by an A/D converter to be used for a digital computation are only an output signal of the flow sensor to be corrected and an output signal of the temperature sensor, and that no output signal of a Vcc voltage divider is in use.
Also, as a device which corrects a converted digital signal or analog signal, the following device is proposed. In an A/D conversion device, a correction value of a digital signal, to which an analog signal is converted, is obtained from the difference in value between a digital signal obtained using a least squares method and a pre-given ideal digital signal. Also, in a D/A conversion device, a correction value is obtained from the difference between the values of three or more digital signals, to which the respective values of different three or more input analog signals are converted, and the values of three or more digital signals to which are converted the exact values of three or more input analog signals corresponding to the respective values of the different three or more input analog signals (for example, refer to JP-A-10-145231).
However, not only the output value of the physical quantity sensor but also the output values of the peripheral circuits are included in the objects which should be corrected in the physical quantity sensor device. In particular, as the D/A converter is further provided in the analog output type of physical quantity sensor device, compared with in the digital output type of physical quantity sensor device, factors causing a variation in the output value of the physical quantity sensor increase. In JP-A-2003-166865 disclosing the analog output type of physical quantity sensor device, the respective characteristic variations of the physical quantity sensor, A/D converter, and D/A converter are converted into one computation expression and collectively corrected, but there are the following two problems.
The first problem is that the respective characteristic variations of the physical quantity sensor, A/D converter, and D/A converter cannot be individually grasped. Because of this, information which can be fed back to the process of manufacturing a physical quantity sensor or an IC (a physical quantity sensor device), on which is mounted the physical quantity sensor, is limited, thus causing a manufacturing management problem. Also, even though the physical quantity sensor shows an anomalous characteristic variation deviating from an error range, it is not possible to detect the characteristic variation of the physical quantity sensor when the characteristics of the A/D converter and D/A converter vary so as to cancel out the anomalous characteristic variation of the physical quantity sensor, thus causing a quality characteristic problem.
The second problem is that when the conversion accuracy of the A/D converter and D/A converter is low, it is not possible to improve the overall accuracy (output characteristic correction accuracy) of the physical quantity sensor device. Because of this, there is the possibility of the need for measures to enhance the overall conversion accuracy of the physical quantity sensor device, such as by using highly accurate A/D converter and D/A converter, increasing the resolution (bits) of the A/D converter and D/A converter, and increasing the order of a computation expression for correcting the output characteristic of the physical quantity sensor device. Because of this, there is the problem of leading to an increase in cost.